Whilst I know nothing much about this (although I did used to have a souped up motor) I would say try to look into importing the stuff from Hong Kong.

Whilst I don't think I can actually help with sourcing this stuff at the moment I always notice that when I go to Hong Kong there are so many sorted cars around it is unbelievable. I presume the accessories are much cheaper, but if you have a Jap car then half the time it will be souped up.